This invention relates generally to a device for maintaining a moving curved surface a constant distance from a stationary point and particularly to a device for moving a kinescope faceplate panel over a detector or light source while maintaining a constant spacing between the panel and the detector or light source.
During the production of picture tubes for color television sets, a black matrix is applied to the inside surface of the faceplate panels. The black matrix consists of parallel black lines which extend vertically as defined by the viewing orientation of the tube. The black lines are spaced at desired intervals leaving transparent glass in the spaces between the matrix lines. The transparent spaces are coated with slurries of materials containing phosphors which emit the three primary colors of red, green, and blue light when impacted by electrons. The three colors of phosphors are alternately applied in a repetitive sequence, such as red, green and blue to all the transparent spaces of the panel. Prior to the application of the phosphors it is desirable to measure the transparent spacings and the matrix line widths to verifty that they are within acceptable dimensional tolerances in order to avoid the expensive application of phosphors to improperly matrixed faceplates.
A system for measuring the width of the transparent spaces, and the combined width of the spaces and black matrix lines is described in Application Ser. No. 466,595 entitled "SYSTEM FOR MEASURING LINE SPACINGS ON A CURVED SURFACE" filed on even date herewith by Frank S. Krufka, now U.S. Pat. No. 4,525,735. In the Krufka system, the faceplate panel is moved with respect to a stationary light source which emits light through the faceplate panel to a detector. The detector provides an output signal which varies from high to low in accordance with the light transmission of the spaces and light opaque nature of the matrix lines on the panel. The matrix bearing surface of the panel is curved, and the light source and detector are stationary with respect to the panel. Accordingly, the distance from the light source to the panel will vary if the panel motion occurs in a plane which is perpendicular to the light path between the source and the detector. There, therefore, is a need for a device for maintaining a constant spacing between a curved surface and a stationary point as the curved surface moves with respect to the point. The instant invention is directed to a device which fulfills this need.